DIGESTION 



135 



from the milky chyle which the lacteals carry after digestion : 

 it consists chiefly of the watery part of the blood, which was 

 not required by the tissues, and is re- 

 turned to the blood by the absorbents 

 or lymphatics. (Bead Note 9.) 



40. Circumstances Affecting Digestion. 

 What length of time is required for 

 the digestion of food? From observa- 

 tions made, in the case of St. Martin, 

 the Canadian already referred to, it has 

 been ascertained that, at the end of two 

 hours after a meal, the stomach is ordi- 

 narily empty. How much time is needed 

 to complete the digestion of food, within 

 the small intestines, is not certain ; but, 

 from what we have learned respecting c 

 their methods of action, it must be evi- 

 dent that it largely depends upon the 

 amount of starch and fat which the 

 food contains. 



FIG. 31. - Two INTESTINAL 

 VILL . MAGNIFIED 100 

 DIAMETERS 



a, &, and c, lacteals ; d, blood- 

 vessels 



9. Absorption of the Lacteals. " The force by which the milky fluid 

 moves upward through the lacteals is very considerable. This has been 

 proved by the distension of the whole system of vessels, including the 

 thoracic duct, even to the occurrence of rupture, when that duct has been 

 tied in an animal a short time before it has been fed. The movement of 

 the fluid thus, in some measure, resembles absorption by the spongioles 

 at the extremities of the roots of trees, and the continuous rising of the 

 sap. The thoracic duct may become diseased, and a serious derange- 

 ment of nutrition take place. In the case of an unfortunate person, 

 who was some years ago exhibited as a curiosity under the name of the 

 * living skeleton,' was illustrated the slow starvation that may thus be 

 produced. Although he was able to take food in abundant supply, he 

 was not nourished by it. Finally he died, and an examination of his 

 body disclosed the fact that the thoracic duct had been obstructed by 

 disease, and absorption by the lacteals was prevented. Hard work 

 directly after a hearty meal is bad practice. Remember the story of the 

 two hounds. They were both fed alike in the morning ; one of them 

 was taken out to run on a hunt, the other was tied up at home. When 

 the master came back from the hunt, both dogs were killed, and their 



40. What can you state as to the time required for digestion ? 



